Justin Timberlake, Matt Lauer, Martha Stewart and the Kennedys have all done it.
They've taken the Ice Bucket Challenge that's helped raise $2.3 million for the national ALS Association since July 29.
That's compared with raising $25,000 in donations during the same time period last year, according to an e-mail from Carrie Munk, association spokeswoman.
Here's how it works: Dump a bucket of ice water over your head and nominate someone else to do the same. Ethel Kennedy nominated President Obama to take the challenge. He's passing but still donating the money.
The challenge is all being done to raise awareness of ALS or amyotrophic lateral sclerosis, better known as Lou Gehrig's disease.
The Ice Bucket Challenge has taken off on social media. People have posted photos and videos of themselves on Facebook and Twitter, using #IceBucketChallenge.